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Knitting machines and methods of knittingKnitting machines and methods of knitting description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070180863, Knitting machines and methods of knitting. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This invention relates to improved knitting machines and methods of knitting. [0002] The present invention is principally concerned with--but is not limited to--flat bed knitting machines. In order to explain fully certain disadvantages which are associated with prior art flat bed knitting machines, and to aid in the explanation of the advantageous features provided by the present invention, it is helpful to briefly review some of the salient features of prior art flat bed knitting machines. [0003] Important aspects of prior art flat bed knitting machines include the needles employed, the needle bed, knitting cams, and yarn feeding devices. [0004] Probably the most important form of knitting needle in the context of flat bed knitting is the latch needle. The latch needle has the advantage of being self acting or loop controlled. For this reason, it is the most widely used knitting needle in weft knitting and is sometimes termed the automatic needle. Precisely manufactured latch needles are today knitting fabrics of high quality at very high speeds. [0005] FIG. 1 depicts a latch needle 10, which has the following important parts: a hook 12 which draws and retains the knitting loop; a latch 14; a rivet or axle 16 of the latch needle 10; a stem 18 which carries the knitted loop in the clearing or rest position; and a butt 20 which enables the movement of the needle 10 by utilising cams. [0006] In order to form a new knitted loop the needle has to be reciprocated between two fixed points, ie, between two dead centres. During a forward movement of the needle the knitted loop, which was formed earlier, is cleared from the hook because the knitted loop slides down inside the hook and hits the latch; this will result in the opening of the needle hook (due to the anti-clockwise rotation of the latch). Further movement of the needle causes the knitted loop to slide off the latch and then down on to the stem. This is the final position of the forward movement of the needle, known in the knitting technology art as the clearing position or clearing height of a needle. [0007] During the backward movement of the needle the hook is closed automatically because the knitted loop which was on the stem slides forwards, contacting and pivoting the latch tightly closed. Before this occurs a new yarn has to be laid across the hook. As the latch needle continues with its downward motion the newly supplied yarn is drawn through the knitted loop. Latch needles thus knit automatically, and the opening and closing of the hook is carried out by the knitted loop without using additional knitting elements. Current practice is to arrange latch needles in the tricks or grooves of a needle bed, as is explained in greater detail below. [0008] Thus, latch needles have to be reciprocated between two fixed dead centres to form new knitted loops, and one complete oscillation of the needle is known as the knitting cycle. The reciprocating movement of the needles is achieved by moving a system of cams on the top surface of a needle bed. [0009] During the early stage of the backward needle movement, a yarn is laid across the opened needle hook area by a yarn feeding element (in flat bed knitting the yarn feeding element is called a yarn carrier). Shortly afterwards, the knitted loop on the needle stem forces the latch to rotate and close the hook due to its relative movement towards the hook. As the needle continues to move backwards the knitted loop moves on to the latch and then is cast off. [0010] During the final stages of the backward needle movement, the yarn in the hook is pulled through the cast off knitted loop, thus forming the new knitted loop and converting, at the same time, the previous knitted loop into a stitch. [0011] Alternatively, compound needles may be used in place of the latch needles with the provision that the compound needle is not self-acting as described above and requires opening and closing during the loop formation cycle. [0012] The function of the needle bed is to hold and guide latch and needles. The needle beds are made out of high quality metal blocks, a representative prior art needle bed 22 being shown in FIG. 2. On one surface of the block 22 parallel grooves 24 of equal width are machined at equal distances. Latch needles are placed inside these grooves and moved mechanically between two dead centres. The grooves are commonly called needle tricks. The distance between two adjacent needle tricks is called the needle space (t). The needle tricks are wider at the top edge, where the needle hook is placed, to accommodate the somewhat bigger knitted loop. This edge also builds the knocking over edge (verge). The shape of the metal block depends on the type of the knitting machine. [0013] Flat bed knitting machines are typically equipped with two flat needle beds arranged in the form of a roof. The important parts of a flat needle bed are shown in FIG. 3, which depicts a latch needle 30 in place in the groove of a needle bed 32. The wall 34 of the groove is shown in FIG. 3, together with the needle security spring 36, needle cover band 38 and knock over jack 40. The needle cover band 38 maintains the knitting needles against the base of the needle bed 32. It also has a braking effect on the knitting needles and prevents them from springing back. [0014] The movement of the latch needles between two dead centres is technically realised by means of inclined metal planes. These operate at a defined distance above the needle bed and act on the butts of latch needles. These inclined planes are called knitting cams and are usually fixed on to a cam plate. FIG. 4 shows the knitting cams, 42, 44, 46. Additionally, FIG. 4 depicts a number of elements which are shared with FIGS. 1 and 2: common numerals are used to denote such shared elements. [0015] The central cam 42 raises the knitting needles. The central cam 42 is also known as the raising cam in the art. The lowering or stitch cams 44, 46 lower the raised knitting needles and prevent the raising needles from overshooting. The stitch cam 44 (on the left hand side of FIG. 4) lowers the knitting needles when the cam plate moves on the needle bed from right to left, as shown in FIG. 4. Meanwhile the other lowering cam 44 acts as a guiding cam. When the cam plate moves on the needle bed from left to right the raised knitting needles are then lowered by the right stitch cam 46. The two elements, the raising cam and the lowering or stitch cams, are employed in all types of knitting machines with latch needles, whether they be circular weft knitting machines or flat bed weft knitting machines, manual or automatic. In general the raising cam and the lowering cams form a track for the needle butt and is thus called the cam track. Only the needles whose butts fall into the cam track can participate in the knitting process. [0016] Prior art flat bed knitting machines are precisely engineered with two needle beds of hardened steel that are arranged in an inverted V-form. In the needle beds, needles are placed inside needle tricks (typically open rectangular grooves precisely cut with a tolerance of about +40 .mu.m to accommodate needles with a tolerance of -40 .mu.m on the top surface of the needle bed). This arrangement facilitates the movement of needles individually and linearly during the knitting process. The introduction of the needle-latch or closing element to open and close the needle hook area simplifies the stitch formation process. The combination of needle tricks and latch needles have paved the way for the creation of complex 3-D structures on these machines. [0017] The three prerequisites for the stitch formation process include the linear movement of the latch needle, the control of the knitted loop during this movement and the delivery of yarn into the open needle hook. In order to move the needles independently, it is necessary that there is a mechanism for their selection. The mechanisms for needle movement (cam plate) and selection are included in a carriage that is reciprocated along the needle beds. The needle movement is achieved using cams and the needle selection mechanism(s) brings the butts of pre-defined needles into the track of the cams. Currently, this is achieved via two techniques. On modern machines additional elements, called needle selection jacks, are positioned below the latch needle; needle beds with extended tricks are used in order to accommodate the selection jacks. One of the techniques is to press down the needle butt into the needle bed by using special cams shortly after the needle has completed the knitting cycle. Such a needle will remain in this position until it is released by its selector jack and the needle butt will not come into contact with the cam track; thus it will remain inactive and, therefore, cannot form a knitted loop. This is known generally as missing and will result in the creation of a float in the knitted structure. The second technique is to position the needle so that its butt is below the cam track soon after the completion of the knitting cycle, again using special cams. In this position the needle will remain idle until its selector jack re-positions the needle so that its butt could follow the cam track. On modem electronic knitting machines the selection mechanism is based on electromagnetic methods, and the selection system has been integrated on to the cam system, ie, the electromagnetic selection system is positioned in front of the knitting cam system. As a result the needles are selected always in advance to the cam system. [0018] Industrial flat-bed knitting machines are constructed with two needle beds that are arranged in the roof form. Latch needles are placed in grooves of the needle beds, and reciprocated between the two fixed dead centres by moving a system of cams on the top surface of each needle bed. The cam systems of the two needle beds are connected to each other with a metal arm, called the bow, and the entire unit is known as the carriage, which describes a transverse reciprocating movement between the left and right hand ends of the needle beds during knitting. The yarn is guided to the needles with a yarn carrier, which is taken along by the bow of the moving carriage. As the yarn carrier traverses under the bow, the yarn path is maintained parallel to the top edges of needle beds. In flat bed knitting machines the yarns are guided to yarn carriers from the sides of the machine (needle beds), so that the yarn path is straight and to avoid interference from moving parts. At least one spring loaded cymbal tensioner is integrated into the yarn path in order to maintain the yarn under tension, and a return spring is fixed next to the yarn package in order to take the excess yarn back at the early stage of the carriage movement towards the yarn guiding side of the needle beds. In some flat bed knitting machines additional take-back springs are provided at the side of the needle beds, in order to assist the yarn take back action. [0019] Ideally, in weft knitting the needles should have only one function, ie, to form stitches, but, in practice, in order to carry out the above function the knitting needles also must pull the required length of yarn from the yarn package. The result is that the run-in yarn tension will be much higher than the yarn unwinding tension at the package, because the yarn has to overcome all the frictional drag along its patch. [0020] The schematic diagram in FIG. 5 demonstrates the path of the yarn on a modern electronic flat-bed knitting machine, shown generally at 50. The knitting machine 50 comprises a yarn carrier 52 delivering yarn 54 to a needle (not shown), yarn guides 56, 58, 60, 62, 64, 66 yarn take-back spring 68, a cymbal tensioner 70 and a yarn package 72. [0021] A transverse reciprocating carriage takes the yarn carrier 52 along with it and thus also influences the run-in-yarn tension; in fact, it causes the run-in-yarn tension to vary during the knitting of alternating courses, which is caused due to the unwinding of unequal lengths of yarn from the yarn package depending on the direction of the carriage movement. Another important factor is the yarn velocity. At the beginning of knitting a new course, the carriage, which takes the yarn carrier along with it, accelerates from zero velocity until it reaches its nominal knitting velocity, and at the opposite end of the needle bed, ie, shortly before the end of that course, it is decelerated and brought to rest. This results in a discontinuous yarn movement. [0022] In order to address the difficulties encountered with adequately delivering an amount of yarn during knitting operations, various positive yarn feed devices have been developed. The basic principle underpinning positive yarn feeding (delivery) is the delivery of a predetermined length of yarn to the needles. The object is to ensure that each row of stitches formed by a given number of needles (called a course in knitting) will be of a constant length of yarn. The positive yarn feeding was first employed in multi-feeder circular knitting machines. It should be noted that needle cylinders are used in conjunction with circular knitting machines, instead of flat needle beds. A needle cylinder is made from a hollow metal cylinder. On circular knitting machines the yarn is delivered to the needles at a constant velocity by using positive feed systems. The yarn delivery velocity is calculated prior to knitting using a simple equation:stitch length.times.the total number of needles=the length of the yarn to be delivered per machine revolution. The positive yarn feeding devices are then adjusted to deliver this amount of yarn to the needles per needle cylinder revolution. [0023] This simple method of yarn delivery is not suitable for delivering yarn on a flat-bed knitting machine due to the discontinuous yarn movement. On a circular knitting machine the distance between yarn feed wheel and the point at which the yarn is delivered to the needles is a constant. In contrast, in flat-bed knitting this distance varies according to the yarn carrier position, which in turn is defined by the carriage position, and, more precisely, by the position of the needle that is knitting. [0024] A positive yarn feed system for a flat-bed knitting machine which is intended, at least in part, to overcome these problems is described in Kennon et al (W R Kennon, T Dias and P Xie, J. Text. Inst., 2000, Part 3, 140). In this system, a positive yarn feed device having a servomotor is employed. Before knitting of a fabric panel commences, a personal computer (PC) is provided with CAD data containing information relevant to the knitting of the fabric panel to be produced, including details of the sketch length, the number of needles the knitting is to span and the required fabric structure. The PC communicates with a microprocessor which in turn controls the servomotor on the positive feed device in accordance with these data. The knitting machine described in Kennon et al is primarily an academic, proof of principle system, and suffers from a number of drawbacks which prevent practical usage for knitting items such as articles of clothing and patterned fabrics. Firstly, the delivery of yarn by the positive feed device can become erroneous if, as is often the case in practice, the knitting operation loses synchronisation with the pre-programmed knitting pattern. Secondly, the feed system of Kennon et al does not properly account for variations in factors such as the coefficient of friction of the yarn and run-in yarn tension. Thirdly, the feed system of Kennon et al is only capable of knitting a very simple fabric comprising rows of stitches of constant stitch length. The machine and methodology of Kennon et al is unable to knit a course with different patterning elements (such as stitches, tuck loops, etc). Clearly, this is a very major obstacle to practical, commercial usage. Continue reading about Knitting machines and methods of knitting... Full patent description for Knitting machines and methods of knitting Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Knitting machines and methods of knitting patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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